86 THE MICROSCOPE AND ITS REVELATIONS. 



CHAPTEK III. 

 ACCESSORY APPARATUS. 



IN describing the various pieces of Accessory Apparatus with which 

 the Microscope may be furnished, it will be convenient in the first place 

 to treat of those which form (when in use) part of the instrument itself, 

 being appendages either to its Body or to its Stage, or serving for the 

 Illumination of the objects which are under examination; and secondly, 

 to notice such as have for their function to facilitate that examination, 

 by enabling the Microscopist to bring the objects conveniently under his 

 inspection. , 



Section 1. Appendages to the Microscope. 



82. Amplifier. It is obvious that if, by the use of a concave lens 

 interposed between the Objective and the Eye-piece, the divergence of 

 the rays, in the course from the former to the latter, be increased, the 

 magnifying power of the instrument will be augmented in proportion; 

 and such an addition (which was long since introduced into Telescopes, 

 and also into the Solar Microscope) has been brought into general use in 

 the United States, having been first made effective by Mr. Tolles. As con- 

 structed by him, the Amplifier is an achromatic concavo-convex lens of 

 small diameter, screwed into the lower end of the draw- tube, so as to be 

 at no great distance behind the objective, the power of which it doubles, 

 without (it is affirmed) producing sensible deterioration of the image. 



ey proved 



distinguishable; and that the 19th band of Nobcrt's ruled plate could be 

 resolved with its aid, by objectives under which without it no resolution 

 could be obtained. 1 It is obvious that if the magnifying power of our 

 Microscopes can be thus doubled, without the strain of eyes, and the loss 

 of light and of definition, produced by deep Eye-piecing, and without 

 the necessity of employing Objectives of inconveniently short focus and 

 great cost, a great advantage will have been gained; while those who 

 wish to possess a graduated range of powers, need only supply themselves 

 with half the number of Objectives needed to give it, since each can be 

 made to do double work (a 1 inch, for example, serving also as a half-inch) 

 without change either of the eye-piece or the focal adjustment. Dr. 

 Wythe, of San Francisco, states that he has obtained very good results by 

 placing a double-concave or a concavo-convex lens of about 6 inches focus, 

 and of as large a diameter as the tube will allow, about 3 inches below the 



1 " American Monthly Journal of Microscopy," Vol. iii. (1878\ p. 38. 



